As a constituent material of a speaker diaphragm, various materials such as a paper material, a polymer (resin) material, a metal material, a ceramic material, and a composite material are used. There are also known diaphragms configured by paper made of a natural fiber or non-woven fabric made of a synthetic fiber. Among the diaphragms, a paper diaphragm made of the natural fiber generally exhibits advantages, as represented by low density, large internal loss, and easy manufacturing thereof. Therefore, paper diaphragms have been widely used.
As a conventional technique in a production method for a paper diaphragm, there is known a technique including a paper making process for subjecting a diaphragm material to paper making, a preliminary drying process for drying the material subjected to the paper making to vaporize moisture, and a press-molding process for press-molding a preliminary molded product obtained by the preliminary drying process (see, for example, Patent literatures 1 and 2 described below).